Study On The Interaction Of Second-order Solitons Propagating In Single-mode Fiber

For the issue of the interaction of optical solitons, there have been many studys focusing on the interaction of fundamental solitons,but few is on the interaction of higher-order solitons. In this paper, the propagation of two neighboring second-order solitons in single-mode fiber is simulated numerically, and the interaction of them is investigated.For picosecond optical solitons, the propagation of two neighboring second-order solitons, neighboring fundamental soliton and second-order soliton, neighboring fundamental soliton and third-order soliton in single-mode fiber is simulated by solving standard nonlinear Schr dinger equation numerically, and the result is explained by using the theory of inverse scattering and the theory of interaction of fundamental solitons. We consider that the two solitons are in phase and out of phase, respectively. Through our numerical calculation, we obtain several main conclusions:First, the two neighboring second-order solitons decay when propagating in single-mode fiber; the group-velocity of the higher amplitude fundamental solitons obtained from decay does not change; the lower amplitude fundamental solitons obtained from decay "attract" (in phase) each other or "repulse" (out of phase) each other.Second, the second-order soliton decays when neighboring fundamental soliton and second-order soliton propagating in single-mode fiber; the group-velocity of the higher amplitude fundamental soliton obtained from decay does not change; the initial fundamental soliton and the lower amplitude fundamental soliton obtained from decay "attract" (in phase) each other or "repulse" (out of phase) each other.Third, when neighboring fundamental soliton and third-order soliton propagating in single-mode fiber, the lowest amplitude fundamental soliton separates from the initial third-order soliton and "attract" (in phase) or "repulse" (out of phase) with the initial fundamental soliton; after the lowest amplitude fundamental soliton separates from the initial third-order soliton, the residual part of third-order soliton gradually develops into pulses with same peak value and they separate from each other during propagation. For femtosecond optical solitons, the propagation of second-order soliton and twoneighboring second-order solitons under the effect of three higher-order effects(third-order dispersion, self-steepening, self-frequency shift) is simulated respectively by solving standard higher-order nonlinear Schr dinger equation numerically, and the result is explained. Through our numerical calculation, we obtain several main conclusions:First, under the effect of higher-order effect, second-order soliton decays during propagation in single-mode fiber; the decay of second-order soliton caused by third-order dispersion can be aggravated by positive initial frequency shift, and restrain by negative initial frequency shift; the ratio of peak power of the lower and higher amplitude fundamental soliton reduces gradually when higher-order nonlinear effect(self-steepening, self-frequency shift) amplifies.Second, the two neighboring second-order solitons decay when higher-order effect exists, but the main factor causing decay is higher-order effect, and yet the interaction of solitons just makes the discipline of decay of two second-order solitons different. The diffrence includes: the decay of two solitons is not synchronous, and two lower(higher) amplitude fundamental solitons are not totally alike.